It is known to provide a mid-turbine frame assembly between high and low pressure turbine (HPT and LPT) rotor assemblies to support bearings and to transfer loads radially outwardly to a core engine casing. The mid-turbine frame assembly typically comprises a mid-turbine frame supporting an annular inter-turbine duct therein. The inter-turbine duct is defined between outer and inner duct walls which are interconnected by a plurality of radial hollow struts, thereby forming an annular hot gas path to convey the working fluid from the HPT to the LPT. The inter-turbine duct and the hollow struts are subjected to high temperatures and therefore cooling air is introduced around the inter-turbine duct and into the hollow struts to cool the same. Secondary air is also used to pressurize and cool the bearings supported by the mid-turbine frame assembly. In conventional cooling air systems for mid-turbine frames, the cooling air is fed to the mid-turbine frame centrally through the LP shaft. As the air travels through the shaft, the air picks up heat. As a result, the air available for cooling and pressuring the seals of the bearings is not as cool as it could be. This may have a detrimental effect on the integrity and durability of the bearing seals. It also imposes constraints on the types of seal that can be used in the turbine section of the engine.
There is thus room for improvement.